1. Field of the Invention
The present invention relates to a magnetic recording medium for use in, e.g., a hard disk drive using the magnetic recording technique, and a magnetic recording/reproducing apparatus using the magnetic recording medium.
2. Description of the Related Art
The recording density of a hard disk drive (HDD) as one type of a magnetic recording/reproducing apparatus is increasing by 60% or more per year, and this tendency presumably continues in the future. Therefore, a magnetic recording head and magnetic recording medium meeting this high recording density are being developed.
A magnetic recording medium contained in a magnetic recording/reproducing apparatus presently put on the market has a structure in which a Co alloy film containing Co as a main component is formed on an Al alloy substrate or glass substrate by sputtering. Since the longitudinal magnetization system is used as a magnetic recording system, an underlayer for orienting the easy axis of magnetization, i.e., the C axis of Co crystal grains having the hcp structure parallel to the substrate is used. An example of this underlayer is a Cr alloy film in which a specific face of the fcc structure is oriented. In addition, a seed layer, e.g., an NiAl seed layer, for decreasing the grain size by growing a specific face of Cr is used. A measure to counter the problem that the holding period of recorded information shortens by thermal decay as the recording density increases is demanded. Therefore, a longitudinal magnetic recording medium is developed in which multiple layers are antiferro-magnetically coupled with each other by a multilayered structure formed by sandwiching a thin Ru film between magnetic films.
Also, as a method more suited to high density, a perpendicular magnetic recording system using perpendicular magnetization in recording is being extensively studied. In this system, the same Co alloy as used in the longitudinal medium is used as a recording layer. However, to perpendicularly orient the C axes of Co crystal grains, amorphous such as Ge or NiTa or an underlayer such as Ti, Ru, Pd, or Pt in which the closest packed plane of hcp or fcc is oriented is used. In addition, to ensure a perpendicular write magnetic field, a soft magnetic layer is formed between the substrate and the underlayer and seed layer and combined with a single pole head, thereby obtaining better perpendicular recording.
To reduce the noise of the perpendicular magnetic recording medium, Jpn. Pat. Appln. KOKAI Publication No. 11-296833, for example, proposes a method by which a double-layered perpendicular magnetic recording layer is used, and the content of a nonmagnetic element in the upper layer is made smaller than that in the lower layer, thereby making the saturation magnetization and magnetic anisotropic energy in the upper layer larger than those in the lower layer.
Furthermore, techniques of controlling thermal decay of the perpendicular magnetic recording medium are also disclosed. Examples currently being studied are a method of forming a Pt film on the surface of a recording layer, and a CGC (Continuous Granular Composite) medium in which a film having a strong magnetic interaction in the film is formed on a CoCrPt-based magnetic film.
To increase the recording/reproduction resolution, it is known to, e.g., shorten the shield gap length of an MR head, reduce the space between the head and the magnetic recording medium, decrease the film thickness in the longitudinal magnetic recording medium, decrease the distance between the head and the backing soft magnetic film in the perpendicular magnetic recording medium, or reduce the coercive force dispersion.
Unfortunately, the conventional magnetic recording media and recording/reproducing apparatuses are unsatisfactory in performance for the purpose of high-density recording, and require further improvements.
As described above, reducing the coercive force dispersion or the like of the magnetic recording medium is presumably advantageous to increase the recording resolution. However, no method capable of further reducing the coercive force dispersion of the current magnetic recording media has been found yet.